Molecular cloud dispersal traced by the ionized carbon 158 μm line

¹ I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
² Green Bank Observatory, 155 Observatory Road, Green Bank, WV 24944, USA
³ University of Maryland, Department of Astronomy, College Park, MD 20742-2421, USA
⁴ Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
⁵ SOFIA Science Center, USRA, NASA Ames Research Center, Moffett Field, CA 94045, USA
⁶ Astronomisches Rechen-Institut, ZfA Universität Heidelberg, Mönchhofstraße 12–14, 69120 Heidelberg, Germany
⁷ Center for Gravitational Waves and Cosmology, West Virginia University, Chestnut Ridge Building, Morgantown, WV26505, USA
⁸ Max-Planck Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁹ Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos 0610, 1270398 Antofagasta, Chile

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 18 March 2026
Accepted: 9 June 2026

Abstract

Feedback from massive stars in the form of radiation and winds impacts the associated host molecular cloud. Not only can feedback compress gas and trigger the formation of dense cores that eventually collapse into new stars, it can also disperse cloud material and lead to the destruction of the cloud. Both processes can operate simultaneously, but their relative timescales and the dominant feedback mechanisms remain subjects of active debate. Recent observations of the ionized carbon [C II] 158 μm line in high-mass star-forming regions have demonstrated that this line is an excellent tracer of the gas dynamics in such environments. Expanding [C II] shells have been detected, along with high-velocity gas escaping the natal cloud through low-density channels. Motivated by these results, we conducted a systematic analysis of spectrally resolved [C II] maps obtained with the Stratospheric Observatory for Infrared Astronomy (SOFIA) towards ten high-mass star-forming regions hosting at least one O-type star. This dataset provides a unique perspective on the influence of stellar feedback on the parent molecular cloud. Across all regions, we identify high-velocity [C II] line wings that typically emerge ~5–30 km s⁻¹ from the systemic velocity of the host cloud. These velocities exceed the cloud’s escape velocity, indicating that this gas is not gravitationally confined. We show that the high-velocity gas exhibits a complex velocity structure and cannot be attributed solely to a single, coherent expanding [C II] bubble. The amount of material in these erosion flows depends on the evolutionary stage of the molecular cloud and its associated H II region. Once the initial bubble around the cluster ruptures, typically after ~0.1 Myr, gas is expelled from the cloud. Estimates of the associated mass ejection rates vary from ~10⁻³ M_⊙ yr⁻¹ for clusters with a single O9V star to 2 × 10⁻² M_⊙ yr⁻¹ for the most massive clusters. The resulting cloud erosion timescales based on these directly observed mass ejection rates typically vary between 2 and 10 Myr after the formation of the first O stars, similar to other indirect measures of molecular cloud lifetimes. These results suggest that stellar feedback is able to remove enough molecular gas to terminate the star formation in the host cloud.